4906. Day-degree, or Degree day : Variation of one degree per day in mean daily temperature, above an adopted standard reference temperature (usually 10oC). The number of degree days for a single day is the actual variation of mean temperature from the standard. The number of degree days is a month, or other interval, is the sum of daily values. When the mean temperature on a given day is equal or lower than the standard than the standard reference temperature, that day is not considered in the monthly total.